Failover in a data center that includes a multi-density server

ABSTRACT

Failover in a data center that includes a multi-density server, where the multi-density server includes multiple independent servers, includes; detecting, by a management module, a failure of one of the independent servers of the multi-density server; identifying, by the management module, a failover target; determining, by the management module, whether the failover target is a non-failed independent server included in the multi-density server; and responsive to determining that the failover target is a non-failed independent server included in the multi-density server, migrating, by the management module, the failed independent server&#39;s workload to another server that is not included in the multi-density server.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priorityfrom U.S. patent application Ser. No. 14/083,539, filed on Nov. 19,2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,methods, apparatus, and products for failover in a data center thatincludes a multi-density server.

2. Description of Related Art

In data centers today, a server having a single rack space form factormay, in fact, house many independent servers. Such a server is referredto as a multi-density server. While independent servers may share someresources of the multi-density server, independent servers within thesame multi-density server may each include separate central processingunits (CPUs), separate primary memories, separate communicationsadapters, separate local power supplies, and so on. Each independentserver may execute a separate and independent operation system anddifferent workloads. Other servers in the data center may interact witheach independent server as if the independent server was a server in asingle rack space form factor. That is, the physical housing of theindependent server does not factor into another servers interaction withthe independent server.

Problems occur, however, in migration for purposes of high availabilityand failover. Migration due to failover is often carried out withrespect to physical affinity. A workload executing on a first server isoften migrated, during failover, to the physically closest availableserver. In multi-density servers, however, a failure of one independentserver often leads, due to the affinity algorithms, to migrating thefailing independent server's workload to another independent server ofthe same multi-density server. Failures, however, in an independentserver often require the entire multi-density server (including allindependent servers) to be taken off-line for repair. Also, a singlefailure detected in one independent server may find be caused byresource failure of the multi-density server that are shared amongst allindependent server. As such, a failure of one independent serverrepresents higher probability of failure in another independent serverin the same multi-density server than a failure in another serverhousing altogether. In each of these examples, migration of workloadfrom one independent server to another within the same multi-densityserver is inefficient and may possibly result in failure to provide highavailability.

SUMMARY OF THE INVENTION

Methods, apparatus, and products for failover in a data centercomprising a multi-density server are disclosed in this specification.The multi-density server includes a plurality of independent servers.Failover in such a data center includes: detecting, by a managementmodule, a failure of one of the independent servers of the multi-densityserver; identifying, by the management module, a failover target;determining, by the management module, whether the failover target is anon-failed independent server included in the multi-density server; and,responsive to determining that the failover target is a non-failedindependent server included in the multi-density server, migrating, bythe management module, the failed independent server's workload toanother server that is not included in the multi-density server. Theforegoing and other objects, features and advantages of the inventionwill be apparent from the following more particular descriptions ofexemplary embodiments of the invention as illustrated in theaccompanying drawings wherein like reference numbers generally representlike parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 sets forth a functional block diagram of an exemplary data centerthan includes a blade environment configured for server failoveraccording to embodiments of the present invention.

FIG. 2 sets forth a block diagram of automated computing machinerycomprising an exemplary computer in the form of a management moduleuseful for failover in a data center that includes a multi-densityserver according to embodiments of the present invention.

FIG. 3 sets forth a flow chart illustrating an exemplary method forfailover in a data center that includes a multi-density server accordingto embodiments of the present invention.

FIG. 4 sets forth a flow chart illustrating an exemplary method forfailover in a data center that includes a multi-density server accordingto embodiments of the present invention.

FIG. 5 sets forth a flow chart illustrating an exemplary method forfailover in a data center that includes a multi-density server accordingto embodiments of the present invention.

FIG. 6 sets forth a flow chart illustrating an exemplary method forfailover in a data center that includes a multi-density server accordingto embodiments of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary methods, apparatus, and products for failover in a data centerthat includes a multi-density server in accordance with the presentinvention are described with reference to the accompanying drawings,beginning with FIG. 1. FIG. 1 sets forth a functional block diagram ofan exemplary data center than includes a blade environment (100)configured for server failover according to embodiments of the presentinvention. Examples of such blade environments may include the BladeSystem from HP, the BladeCenter® from IBM, and others as will occur tothose of skill in the art.

The blade environment (100) in the example of FIG. 1 includes a bladeserver chassis (106) housing a number of blade servers (118-127). Bladeservers (118-127) are installed in blade server chassis (106). A bladeserver chassis is an enclosure in which blade servers as well as otherelectrical components are installed. The chassis provides cooling forservers, data communications networking connections, input/output deviceconnections, power connections, and so on as will occur to those ofskill in the art. One example blade server chassis is IBM's BladeCenter.An IBM BladeCenter E includes 14 blade slots, a shared media tray withan optical drive, floppy drive, and Universal Serial Bus (‘USB’) port,one or more management modules, two or more power supplies, tworedundant high speed blowers, two slots for Gigabit Ethernet switches,and two slots for optional switch or pass-through modules such asEthernet, Fibre Channel, InfiniBand or Myrient 2000 modules.

A server, as the term is used in this specification, refers generally toa multi-user computer that provides a service (e.g. database access,file transfer, remote access) or resources (e.g. file space) over anetwork connection. The term ‘server,’ as context requires, refersinclusively to the server's computer hardware as well as any serverapplication software or operating system software running on the server.A server application is an application program that accepts connectionsin order to service requests from users by sending back responses. Aserver application can run on the same computer as the clientapplication using it, or a server application can accept connectionsthrough a computer network. Examples of server applications include fileserver, database server, backup server, print server, mail server, webserver, FTP servers, application servers, VPN servers, DHCP servers, DNSservers, WINS servers, logon servers, security servers, domaincontrollers, backup domain controllers, proxy servers, firewalls, and soon.

Blade servers are self-contained servers, designed for high density. Asa practical matter, all computers are implemented with electricalcomponents requiring power that produces heat. Components such asprocessors, memory, hard drives, power supplies, storage and networkconnections, keyboards, video components, a mouse, and so on, merelysupport the basic computing function, yet they all add bulk, heat,complexity, and moving parts that are more prone to failure thansolid-state components. In the blade paradigm, most of these functionsare removed from the blade computer, being either provided by the bladeserver chassis (DC power) virtualized (iSCSI storage, remote consoleover IP), or discarded entirely (serial ports). The blade itself becomessimpler, smaller, and amenable to dense installation with many bladeservers in a single blade server chassis.

In the example of FIG. 1, at least one of the blade servers (118) is amulti-density server (104). A multi-density server is a server housingtypically configured to include hardware for only a single server, butactually including a plurality of independent servers. That is, amulti-density server may include computer hardware that supports two ormore independent servers, while the computer hardware is actually storedin a single server's housing. For example, a multi-density server may beof a single rack unit (IU) form factor configured for installation in asingle slot of a server chassis. One example of a multi-density serverconfigured in a single rack unit housing is a blade server. Such a formfactor typically contains computer hardware that supports only a singleindependent server. A multi-density server, by contrast, may includecomputer hardware that supports multiple independent servers (108 a, 108b). Such computer hardware may include one set of primary memory, suchas Random Access Memory (RAM) (168 a, 168 b), for each independentserver, one CPU (156 a, 156 b) for each independent server, separatecommunications adapters and communications ports for each independentserver, and the like. Each independent server (108 a, 108 b) in theexample multi-density server (104) of FIG. 1 is executing a workload(102 a, 102 b). The multi-density server may also include some computerhardware that, unbeknownst to each independent server's operating system(156 a, 156 b) is actually shared between the independent servers. Avirtual machine is not an independent server as the term is used in thisspecification. Computer hardware that supports execution of a virtualmachine is, in fact, virtualized to some extent while an independentserver relates to non-virtualized hardware that is independent ofanother server's hardware within the same housing. Effectively, two ormore computers with all computer hardware forming each computer areincluded inside a single housing of a multi-density server which isnormally configured to include only a single computer's hardware.

In addition to the blade servers (109-127), the blade server chassis(104, 106) in the example of FIG. 1 also house several other electricalcomponents including a power supply (132), a data communications router(130), a patch panel (134) a RAID array (136), a power strip (138) and amanagement module (152).

A management module is an aggregation of computer hardware and softwarethat is installed in a data center to provide support services forcomputing devices, such as blade servers. Support services provided bythe management module (152) include monitoring health of computingdevices and reporting health statistics to a system management server,power management and power control, save and restore configurations,discovery of available computing devices, event log management, memorymanagement, and so on. An example of a management module that can beadapted for use in systems configured for server failover according toembodiments of the present invention is IBM's Advanced Management Module(‘AMM’). The management module in the example of FIG. 1 may beconfigured to carry out server failover according to embodiments of thepresent invention by detecting a failure of one of the independentservers, such as independent server (108 a), of the multi-density server(104). The management module (152) typically is unaware that such aserver is in fact a member of a multi-density server as each independentserver may be configured with separate, independent communicationsadapters which may be utilized to identify separate servers.

Responsive to the detection of failure, the management module (152) mayidentify a failover target. A failover target as the term is used inthis specification is a server or other computer to which a workload maybe moved from a failing server. In embodiments in which the managementmodule (152) identifies failover targets based on physical affinity, themanagement module (152) may identify as a failover target, anotherindependent server within the same multi-density server as the failingindependent server.

To that end, the management module (152) may be further configured todetermine whether the failover target is a non-failed independent server(108 b) included in the multi-density server (104). There are a varietyof ways for the management module (152) to determine whether thefailover target is another independent server within the multi-densityserver (104). Many of these ways are described below in greater detailwith respect to FIG. 6.

Responsive to determining that the failover target is a non-failedindependent server (108 b) included in the multi-density server, themanagement module (152) may migrate the failed independent server'sworkload to another server (119-127) that is not included in themulti-density server. In this way, the management module insures thatany workload migrated away from a failing server is not migrated toanother independent server within the same multi-density server (104).

The arrangement of servers and other devices making up the exemplarysystem illustrated in FIG. 1 are for explanation, not for limitation.Data processing systems useful according to various embodiments of thepresent invention may include additional servers, routers, otherdevices, and peer-to-peer architectures, not shown in FIG. 1, as willoccur to those of skill in the art. Networks in such data processingsystems may support many data communications protocols, including forexample TCP (Transmission Control Protocol), IP (Internet Protocol),HTTP (HyperText Transfer Protocol), WAP (Wireless Access Protocol), HDTP(Handheld Device Transport Protocol), and others as will occur to thoseof skill in the art. Various embodiments of the present invention may beimplemented on a variety of hardware platforms in addition to thoseillustrated in FIG. 1.

Failover in a data center that includes a multi-density server inaccordance with the present invention is generally implemented withcomputers, that is, with automated computing machinery. In the system ofFIG. 1, for example, all the blade servers, multi-density servers, andmanagement module are implemented to some extent at least as computers.For further explanation, therefore, FIG. 2 sets forth a block diagram ofautomated computing machinery comprising an exemplary computer in theform of a management module (152) useful for failover in a data centerthat includes a multi-density server according to embodiments of thepresent invention. The computer (152) of FIG. 2 includes at least onecomputer processor (156) or ‘CPU’ as well as random access memory (168)(‘RAM’) which is connected through a high speed memory bus (166) and busadapter (158) to processor (156) and to other components of the computer(152).

Stored in RAM (168) is a management module application (153), a moduleof computer program instructions that, when executed, causes themanagement module (152) to operate for failover in a data center thatincludes a multi-density server (104) according to embodiments of thepresent invention. The example multi-density server (104) of FIG. 2includes a plurality of independent servers (108 a, 108 b) and each isexecuting a separate workload (102 a, 102 b).

The management module application (153) may carry out failover accordingto embodiments of the present invention by detecting a failure of one ofthe independent servers (108 a) of the multi-density server (104);identifying a failover target; determining whether the failover targetis a non-failed independent server (108 b in this example) included inthe multi-density server (104); and, responsive to determining that thefailover target is a non-failed independent server (108 b) included inthe multi-density server (104), migrating the failed independentserver's workload (102 a) to another server (182) that is not includedin the multi-density server (104).

Also stored in RAM (168) is an operating system (154). Operating systemsuseful in management modules configured for failover in a data centerthat includes a multi-density server according to embodiments of thepresent invention include UNIX™, Linux™, Microsoft XP™, AIX™, IBM'si5/OS™, and others as will occur to those of skill in the art. Theoperating system (154) and management module application (153) in theexample of FIG. 2 are shown in RAM (168), but many components of suchsoftware typically are stored in non-volatile memory also, such as, forexample, on a disk drive (170).

The management module (152) of FIG. 2 includes disk drive adapter (172)coupled through expansion bus (160) and bus adapter (158) to processor(156) and other components of the management module (152). Disk driveadapter (172) connects non-volatile data storage to the managementmodule (152) in the form of disk drive (170). Disk drive adapters usefulin management modules configured for failover in a data center thatincludes a multi-density server according to embodiments of the presentinvention include Integrated Drive Electronics (‘IDE’) adapters, SmallComputer System Interface (‘SCSI’) adapters, and others as will occur tothose of skill in the art. Non-volatile computer memory also may beimplemented for as an optical disk drive, electrically erasableprogrammable read-only memory (so-called ‘EEPROM’ or ‘Flash’ memory),RAM drives, and so on, as will occur to those of skill in the art.

The example management module (152) of FIG. 2 includes one or moreinput/output (‘I/O’) adapters (178). I/O adapters implementuser-oriented input/output through, for example, software drivers andcomputer hardware for controlling output to display devices such ascomputer display screens, as well as user input from user input devices(181) such as keyboards and mice. The example management module (152) ofFIG. 2 includes a video adapter (209), which is an example of an I/Oadapter specially designed for graphic output to a display device (180)such as a display screen or computer monitor. Video adapter (209) isconnected to processor (156) through a high speed video bus (164), busadapter (158), and the front side bus (162), which is also a high speedbus.

The exemplary management module (152) of FIG. 2 includes acommunications adapter (167) for data communications with other servers(182) and for data communications with a data communications network(100). Such data communications may be carried out serially throughRS-232 connections, through external buses such as a Universal SerialBus (‘USB’), through data communications networks such as IP datacommunications networks, and in other ways as will occur to those ofskill in the art. Communications adapters implement the hardware levelof data communications through which one computer sends datacommunications to another computer, directly or through a datacommunications network. Examples of communications adapters useful inmanagement modules configured for failover in a data center thatincludes a multi-density server according to embodiments of the presentinvention include modems for wired dial-up communications, Ethernet(IEEE 802.3) adapters for wired data communications, and 802.11 adaptersfor wireless data communications.

For further explanation, FIG. 3 sets forth a flow chart illustrating anexemplary method for failover in a data center that includes amulti-density server according to embodiments of the present invention.The method of FIG. 3 may be carried out in a data center similar to thatof FIG. 1 which includes a multi-density server similar to that of FIG.2. The multi-density server (104) includes a plurality of independentservers (108 a, 108 b).

The method of FIG. 3 includes detecting (302), by a management module(152), a failure (312) of one of the independent servers (108 a) of themulti-density server (104). Detecting (302) a failure (312) of one ofthe independent servers (108 a) of the multi-density server (104) may becarried out in variety of ways. The management module (152) may receivea notification via an out-of-band bus from a service processor, such asa baseboard management controller (BMC), dedicated to the independentserver that indicates a failure. Such an indication of failure may be anindication of an actual or possible failure. The management module (152)may also periodically ping the operating system of the independentserver to check the status of the server. An indication of a failure maybe result if a ping is not answered or if the ping is answered with sucha failure notification. Readers of skill in the art will recognize thatthere are many ways to detect a failure of a server and each such way iswell within the scope of embodiments of the present invention.

The method of FIG. 3 also includes identifying (304), by the managementmodule (152), a failover target (314). Identifying (304) a failovertarget (314) may be carried out by identifying a server physicallyproximate to the failing server and available to received migratedworkloads. In some embodiments, such a server may be designated in apool of available failover targets.

The method of FIG. 3 also includes determining (306), by the managementmodule (152), whether the failover target (314) is a non-failedindependent server (108 b) included in the multi-density server (104).Determining (306) whether the failover target (314) is a non-failedindependent server (108 b) included in the multi-density server (104)may be carried out in various ways, many of which are described below ingreater detail with respect to FIG. 6.

If the failover target (314) is not a non-failed independent server (108b) included in the multi-density server (104), the method of FIG. 3continues by migrating (310), by the management module (152), the failedindependent server's (108 a) workload (102 a) to another server (105)that is not included in the multi-density server (104). If, however, thefailover target (312) is a non-failed independent server (108 b)included in the multi-density server (104), the method of FIG. 3continues by migrating (308), by the management module (152), the failedindependent server's (108 a) workload (102 a) to another server (105)that is not included in the multi-density server (104). That is, themanagement module (152) selects a server that is not included in themulti-density server as a target for the failover. The management module(152) again may utilize an affinity algorithm or criteria in determiningwhich target, not included in the multi-density server, to select beforemigrating the workload.

For further explanation, FIG. 4 sets forth a flow chart illustrating anexemplary method for failover in a data center that includes amulti-density server according to embodiments of the present invention.The method of FIG. 4 may be carried out in a data center similar to thatof FIG. 1 which includes a multi-density server similar to that of FIG.2. The multi-density server (104) includes a plurality of independentservers (108 a, 108 b). The method of FIG. 4 is similar to the method ofFIG. 3 in that the method of FIG. 4 includes detecting (302) a failure(312) of one of the independent servers (108 a) of the multi-densityserver (104), identifying (304) a failover target (314), determining(306) whether the failover target (314) is a non-failed independentserver (108 b) included in the multi-density server (104), and if thefailover target (312) is a non-failed independent server (108 b)included in the multi-density server (104), migrating (308) the failedindependent server's (108 a) workload (102 a) to another server (105)that is not included in the multi-density server (104).

The method of FIG. 4 differs from the method of FIG. 3, however, in thatwhile or after migrating (308) the failed independent server's workload(102 a), the method of FIG. 4 includes by migrating (402), by themanagement module (152), workload of all non-failed independent servers(108 b) of the multi-density system (104) to a server (105) not includedin the multi-density server. Once one independent server of amulti-density server has failed, it may be necessary to take the entiremulti-density server offline for maintenance or repair. To that end,rather than waiting until a request from a system administrator, themanagement module may preemptively migrate (402) workloads (102 b) ofall non-failed independent servers to another server that is notincluded in the multi-density server. In other embodiments, a failure ofone independent server may be indicative of a failure in themulti-density server itself, in the hardware of the server rack thatsupports the multi-density server, or in some other way related to themulti-density server as a whole. In this way, the management module maybe configured migrate (308, 402) all workload from all independentservers of the multi-density server to another server once a failurefrom just one of the independent servers is detected.

For further explanation, FIG. 5 sets forth a flow chart illustrating anexemplary method for failover in a data center that includes amulti-density server according to embodiments of the present invention.The method of FIG. 5 may be carried out in a data center similar to thatof FIG. 1 which includes a multi-density server similar to that of FIG.2. The multi-density server (104) includes a plurality of independentservers (108 a, 108 b). The method of FIG. 5 is similar to the method ofFIG. 3 in that the method of FIG. 5 includes detecting (302) a failure(312) of one of the independent servers (108 a) of the multi-densityserver (104), identifying (304) a failover target (314), determining(306) whether the failover target (314) is a non-failed independentserver (108 b) included in the multi-density server (104), and if thefailover target (312) is a non-failed independent server (108 b)included in the multi-density server (104), migrating (308) the failedindependent server's (108 a) workload (102 a) to another server (105)that is not included in the multi-density server (104).

The method of FIG. 5 differs from the method of FIG. 3, however, in thatprior to migrating (308) the failed independent server's (108 a)workload (102 a) to another server (105), the method of FIG. 3 includesmigrating (502), by the management module (152), the failed independentserver's (108 a) workload (102 a) to the non-failed independent server(108 b) included in the multi-density server until another server (105)not included in the multi-density server (104) is available as afailover target. From time to time and for various reasons, it ispossible that each server set aside in a pool of available failovertargets is unavailable to be utilized as a failover target. To that end,rather than leaving the workload (102 a) not executing or executing on afailed server (108 a), the management module (152) may migrate (502) theworkload (108 a) to another independent server (108 b) of themulti-density server (104) for a time. When another server becomesavailable as a failover target, the management module (152) may migrate(308) the workload (102 a) to that server (105).

For further explanation, FIG. 6 sets forth a flow chart illustrating anexemplary method for failover in a data center that includes amulti-density server according to embodiments of the present invention.The method of FIG. 6 may be carried out in a data center similar to thatof FIG. 1 which includes a multi-density server similar to that of FIG.2. The multi-density server (104) includes a plurality of independentservers (108 a, 108 b). The method of FIG. 6 is similar to the method ofFIG. 3 in that the method of FIG. 6 includes detecting (302) a failure(312) of one of the independent servers (108 a) of the multi-densityserver (104), identifying (304) a failover target (314), determining(306) whether the failover target (314) is a non-failed independentserver (108 b) included in the multi-density server (104), and if thefailover target (312) is a non-failed independent server (108 b)included in the multi-density server (104), migrating (308) the failedindependent server's (108 a) workload (102 a) to another server (105)that is not included in the multi-density server (104).

The method of FIG. 6 differs from the method of FIG. 3, however, in thatin the method of FIG. 6, determining (306) whether the failover targetis a non-failed independent server (108 b) included in the multi-densityserver (104) includes identifying (602) one or more independent serversin the multi-density server. As mentioned above, a management module maynot be configured with the knowledge that any particular server is anode of a multi-density server. To that end, the management module mustidentifying (602) those independent servers in the multi-density server(104) to determine (304) whether the failover target is included in thesame multi-density server as the failed independent server (108 a).

The method of FIG. 6 includes various ways to identify (602) independentservers of the multi-density server. The method of FIG. 6, for example,includes identifying (604), in dependence upon timestamps, serverspowered on at the same time as independent servers in the multi-densityserver. Servers powered on at exactly or nearly exactly the same timemay be inferred to be within the same multi-density server as suchservers likely share the same server housing power supply.

The method of FIG. 6 also includes identifying (606) servers having asame slot location in a server rack as independent servers in themulti-density server. Although in some environments the managementmodule is configured with such information in other environments, themanagement module may request such information from a chassis managementmodule or the independent servers themselves.

The method of FIG. 6 also includes identifying (608) servers within apredefined proximity to one another based on timing of pings to bothsystems as independent servers in the multi-density server. A server maysend a data communications ‘ping’ to one or more servers. A ping may bedescribed in terms of the time required for a very short datacommunications message to be sent to a server and returned from theserver. The management module may be configured to infer that two ormore servers having the same or nearly the same amount of ping time arewithin the same multi-density server.

The method of FIG. 6 also includes identifying (610) servers within apredefined proximity to one another based on a trace route of a ping. Atrace route may be utilized to count network hops, or otherwise providenetwork route information, between the management module and a server.By determining that two or more servers have the same or nearly the sametrace routes, the management module may infer that the servers areincluded in the same multi-density server.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A method of failover in a data center comprisinga multi-density server, the multi-density server comprising a pluralityof independent servers, the method comprising: detecting, by amanagement module, a failure of one of the independent servers of themulti-density server; identifying, by the management module, a failovertarget; determining, by the management module, whether the failovertarget is a non-failed independent server included in the multi-densityserver; and responsive to determining that the failover target is anon-failed independent server included in the multi-density server,migrating, by the management module, the failed independent server'sworkload to another server that is not included in the multi-densityserver; and migrating, by the management module, workload of allnon-failed independent servers of the multi-density system to a servernot included in the multi-density server.
 2. The method of claim 1further comprising: responsive to determining that the failover targetis a non-failed independent server included in the multi-density server,migrating, by the management module, the failed independent server'sworkload to the non-failed independent server included in themulti-density server until another server not included in themulti-density server is available as a failover target.
 3. The method ofclaim 1 wherein determining whether the failover target is a non-failedindependent server included in the multi-density server furthercomprises identifying one or more independent servers in themulti-density server by one of: identifying, in dependence upontimestamps, servers powered on at the same time as independent serversin the multi-density server; identifying servers having a same slotlocation in a server rack as independent servers in the multi-densityserver; identifying servers within a predefined proximity to one anotherbased on timing of pings to both systems as independent servers in themulti-density server; and identifying servers within a predefinedproximity to one another based on a trace route of a ping.
 4. The methodof claim 1, wherein the multi-density server comprises a single rackunit form factor configured for installation into a single slot of aserver chassis.
 5. The method of claim 4, wherein the multi-densityserver comprises a blade form factor for a single slot of a blade serverchassis.